The present invention relates to a base fabric for use in an airbag and, more particularly, to an airbag base fabric which is thin and lightweight and is thus effective in reducing size and weight of an airbag module.
Conventionally, a base fabric for use in an airbag of an airbag module is normally a woven fabric made of synthetic filament yarns having fineness from 420 denier to 630 denier and coated with an elastomer or the like.
The conventional base fabric for use in an airbag, which is made of filament yarns having fineness of 420-630 denier, is quite thick because the woven fabric itself is thick and is additionally coated with resin. Since the folded airbag therefore has a large volume and is heavy, the conventional base fabric is not suitable for reduction in size and weight of the airbag module.
Especially recently, a head protective side airbag disposed along a roof side rail has been employed widely. Since there is a small space for accommodating an airbag along the roof side rail, the further reduction in size is required.
It is an object of the present invention to solve the conventional problem and to provide an airbag base fabric which is thin and lightweight and is thus excellent to be accommodated in a small space, so that it is effective in reducing size and weight of an airbag module.
An airbag base fabric of the present invention is composed of thermoplastic synthetic filament yarns, wherein the filament yarn has a strength of 7.0 g/denier or more and fineness of 200-250 denier.
The thin filament yarns, fineness of which is 200-250 denier, enables to provide an airbag base fabric which is thin and lightweight, can be easily folded, and is thus excellent to be accommodated. Since the filament yarns are thin, the weave pattern or density is fine, thereby making the air permeability low. Gas leakage can be prevented even without resin coating or only with a thin coating. This improves the surface smoothness and can further reduce the size of the airbag.
If the filament yarns are too thin, the strength of the obtained airbag base fabric may be insufficient. According to the present invention, however, since the filament yarns having yarn strength of 7.0 g/denier or more are employed, the reduction in strength due to fineness is prevented.
Preferably employed as filament yarns are polyamide yarns or polyester yarns. By weaving such filament yarns with the number of 50 yarns/inch or more, an airbag base fabric having smooth surface can be obtained which has high strength and quite low permeability even under high pressure.
Hereinafter, an embodiment of the present invention will be described.
Examples of filament yarns composing an airbag base fabric of the present invention are polyamide yarns and polyester yarns, preferably, polyamide yarns of nylon or the like.
In the present invention, the filament yarn has yarn strength exceeding 7.0 g/denier and fineness from 200 denier to 250 denier.
A filament yarn having the yarn strength less than 7.0 g/denier can not provide enough strength. Especially, the yarn strength is preferably 7.5 g/denier or more. In the present invention, the yarn strength of the filament yarn is hard to set at 9.7 g/denier or more because of its fine fabrication. Therefore, the preferable yarn strength is in a range of 7.5 to 9.7 g/denier.
In the present invention, if the filament yarn has fineness of 250 denier or more, the thinning and lightening of the airbag by making the filament yarn fine can not be expected. On the other hand, if the filament yarn has fineness of less than 200 denier, it can not provide enough strength, so that the above-mentioned filament yarn is not preferable. The most preferable fineness is 210 denier.
The filament yarn is preferably composed of 34-68 filaments, each having 3.1-6.2 denier.
The filament less than 3.1 denier can not provide sufficient filament strength. Accordingly, even when a large number of such filaments is gathered to form a filament yarn of 200-250 denier, the filament yarn may not have yarn strength of 7.0 g/denier or more. On the other hand, if the filament exceeds 6.2 denier, the number of filaments required to form a filament yarn of 200-250 denier is too small and the obtained filament yarn has undesirably high rigidity and high air permeability, so that the above-mentioned filament is not preferable.
In the present invention, the way of weaving the woven fabric composed of such filament yarns is normally plain weaving, but may be Jacquard weaving or hollow weaving.
The number of the filament yarns in the woven fabric is preferably 50 yarns/inch or more. If the number of the filament yarns is less than 50 yarns/inch, the obtained base fabric can not provide enough strength and enough permeation resistance. On the other hand, if the number of the filament yarns is too much, it increases the rigidity of the base fabric, so that it is hard to fold the obtained airbag and a larger package is required. Normally, the number of the filament yarns is preferably in a range from 68 to 75 filaments/inch.
The woven fabric according to the present invention may be treated by heat setting and/or calendering so as to allow the thickness to be thinner. These treatments further reduce the air permeability.
By using the aforementioned filament yarns with the aforementioned number thereof, and if necessary, by treatment of heat setting and/or calendering, the woven fabric forming the base fabric of the present invention is made to have a thickness of 0.15-0.25 mm preferably and to satisfy the condition that the quantity of airflow measured at 124.5 Pa is 0.8 cm3/cm2/sec or less in accordance with Fragile tester.
Since the woven fabric itself has quite low gas or air permeability, the woven fabric can be used as the airbag base fabric without resin coating. In the present invention, the woven fabric may be treated with resin coating of elastomer resin, such as silicone resin. In this case, since the woven fabric of this invention has quite low gas permeability, the amount of the coating resin can be significantly reduced as compared to the conventional one, that is, 5-25 g/m2 of the coating resin will be enough. Thus, the reduced amount of the coating resin does not make the thickness of the base fabric too thick and heavy, and allows easy folding of the airbag.
The airbag base fabric of the present invention can be effectively used for the airbags of various types, such as a driver""s airbag and a front passenger""s airbag, and is particularly suitable for a head protective airbag to be accommodated adjacent to a roof side rail having a small accommodating space.